Blackcat

Member
Mar 9, 2007
138
0
Okay I am in the process of doing the top end on my bike. After taking off the cylinder I noticed that the piston is scored all to hell. I inspected the cylinder and there where very very tiny groves in it. I'm going to take it up to the shop tomarrow and see what they say about. But to my question. What am I looking for when inspecing a lower bearing. I have some side to side movement. And as far as up and down movement I have some but it's so small that it's hard to notice. But if I hold the rod a certain way there is no movement. So what exactly is it that I'm looking for when examining the lower bearings. Also does anyone know how much it would cost (roughly) to put a new bearing in the bottom end if I took the motor out of the bike and took it up to the shop. Thanks in advance.
 

adam728

Member
Aug 16, 2004
1,011
0
Side to side play is normal, you should be able to find a spec for the proper amount.

There should be NO play in the vertical direction. Sounds like it might be time for a lower end rebuild.
 

KX'er

Member
Oct 12, 2000
140
0
I've been running mine for awhile with the exact movement that you state. so far so good. But I've been getting a bit of vibration in the pegs lately, so I'll probably need to do a bottom end soon...
 

whenfoxforks-ruled

Old MX Racer
~SPONSOR~
Oct 19, 2006
8,129
2
Merrillville,Indiana
I have had good success with the lower end bearing by checking with the plastic end of a large screwdriver.Hold the rod up with one hand and hit it with the plastic,then do it again with no upward tension,if you hear a difference or a little "ting" there is play and time for crank rebuild. The sad part is I only know one person that presses and aligns properly,Eric Gorr dba Forwardmotion.com! This is a press fit,I have and everybody else aligned the crank by using a hammer,bad method,the pressfit is ruined once it is spun,time to weld it,it will jump back to its pressed position. Purchasing complete units rebuilt or new is no guarantee also,crap happens! A good case separator will run a hundred bucks or so,and worth every penny as opposed to beating with a hammer. You could take a plate of metal,drill some alignment holes and 2 old c clamps and adapt to the plate. Use your case bolts to hold in place,weld the c clamp nuts to the plate and use the screw to pop the cases apart,Good luck!
 

84cr125

Member
Apr 8, 2007
292
0
ther should be absolutely no up and down movelment. If there is think of it like this when the crank moves the vertical play will come in and the piston will move closer to the spark plug and the piston will comecloser to the bottom end cases.
 

76GMC1500

Uhhh...
Oct 19, 2006
2,142
1
If your connecting rod big end bearing is out, you have to break apart the crankshaft to replace it. By this point, it's actually cheaper to buy an aftermarket crank. For about $200 you can get the crank, rod, rod bearing, and main bearings. For that same price, you could pay just the labor to have the crank broken apart, reassembled, and trued.
 

84cr125

Member
Apr 8, 2007
292
0
i doubt that, i baught my connecting rod(rot rod) for $120 canadian, and had it assembleb for about $30. so it cost me $150 canadian to get my crank redone.
 
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